1. Field of the Invention
The present invention relates to a detection device and a detection method for reading an ID of an RFID tag, and particularly to an ID detection device and an ID detection method for steadily reading information from plural RFID tags closely lined up one another.
2. Description of the Related Art
In recent years, wireless data carriers of a certain kind or so-called RFID tags have come into use. In each of those RFID tags, a unique ID is set, an information-rewritable memory area is included, and reading of the ID and/or writing and reading of arbitrary information can be wirelessly carried out without contact.
For example, RFID tags having unique IDs are bonded to or incorporated into posted goods or delivered goods, respectively, to identify individual moving goods. If IDs of a large number of RFID tags can be read all at once, efficiency of identification work improves. A method has hence been proposed (e.g., Jpn. Pat. Appln. Laid-Open Publication No. 2005-135354). In the method, for example, posted goods or the like with RFID tags attached are put in a predetermined contained box such that the RFID tags are arranged in a row with their own maximum gain directions aligned with one another. This container box and a transmission/reception antenna (RW antenna) are positioned such that the aligned maximum gain directions of the RFID tags and a maximum gain direction of the transmission/reception antenna are parallel to one another. Thus, the IDs of the large number of RFID tags are read all at once.
There has been another proposal (e.g., Jpn. Pat. Appln. Laid-Open Publication No. 2005-5876) for a method in which a container box containing plural posted goods with RFID tags attached is opposed to a transmission/reception antenna, to read IDs of the plural RFID tags all at once. In the method, a reflection plate is positioned to be opposed to the transmission/reception antenna, to reflect an inquiry electric wave radiated from the transmission/reception antenna. Thus, a radiation area of the inquiry electric wave is extended to be broader than an identifiable area.
According to the techniques described above, however, the inquire electric wave can hardly enter into between crowded wireless tags if a lot of wireless tags are arranged close to one another. In particular, there are serious difficulties in reading an ID of an RFID tag positioned in the center of those crowded tags.